Chinese Journal of Physiology

THYROID AND HAIR GROWTH 59

Age. Tair grows slowly during the first 44 to 65 days after birth, while from 71 to 260 days the rate of hair growth is faster (table 1), indicating that the age factor is not significant except in very young

Days for full growth

Age 60 100 140 180 220 Days '260

Fig. 1. Graph showing the influence of sex and age on the rate of full hair growth in albino rats on normal diet.

Partial feeding. As will be seen from the percentage distribution of the hair growth rates in normal and under-fed animals, under-feeding definitely retards hair growth.

Acceleration Normal rate Retardation

(mean-—2#) (meant+3H) (mean+8F) I. Normal feeding 20 (84) 65 (107) 15 (26) TI. Partial feeding 0 46 ( 19) 54 (22)

(The figures in parentheses give the number of observations.) Whereas 15 per cent of normal animals have hair growth rates exceeding the normal mean+3H (26-+6 days), 54 per cent of partially fed animals have retarded rates. The other groups are affected accordingly.

It is obvious that even with normal feeding considerable individual differences in hair growth exist. To what are these differences due? The most probable factors are either nutritional or endocrine, and we believe that these are related and that the particular internal secretion involved is the thyroid.

The distribution of the partial feeding rates compared with the

mean partial feeding rate (4149, days) is as follows. Mean partial

Acceleration feeding rate Retardation III. Partial feeding 54, (14) 87 (15) 29 (12)